The Indonesian national flag is called "Sang Saka Merah Putih." As
provided for in Article 35 of the 1945 Constitution, the flag is made up
of two colors, red on top of white. Its width is two-thirds of its
length, or two meters by three meters. It is hoisted in front of the
presidential palace, of government buildings and Indonesian missions
abroad. The first flag was courageously flown amidst Japanese occupation
forces on the day Indonesia's independence was proclaimed. Since then it
has been hoisted at independence day commemorations in front of the
presidential palace in the capital city of Jakarta. This historical
flag, or "bendera pusaka," was flown for the last time on August 17,
1968. Since then it has been preserved and replaced by a replica woven
of pure Indonesian silk.
From www.deplu.go.id/background/republic/republic.htm located by Jarig Bakker, 17 May 1999

The flag of Indonesia is based on the flag of the Majapahit Empire on Java at the end of the 13th century. This had nine stripes red and white, and is nowadays used as jack.

In 1922 Indonesian students in Leiden (The Netherlands) adopted a flag red over white for their association, and had the head of a banteng (bull) in the centre. In 1928 it was hoisted by the Partai Nasional Indonesia in Bandung. One year later the first plain red over white flag was hoisted during a student congress in Batavia (nowadays Jakarta).

When the independence of Indonesia was proclaimed at 17 August 1945 in front of Soekarno's house at Pegangsaan Oost 56 in Djakarta, the flag was hoisted:

"It was a simple ceremony. But the lack of pomp and splendour was compensated by our hope. I walked to the microphone stolen from a Japanese radio station and read the Proclamationshort and concise. My wife [Fatmawati] made a flag of two pieces of cloth. A white piece of cloth and a red piece of cloth sewn together by hand. It was the first official flag of the Republic. The staff was a piece of bamboo put in the ground short before. It was a primitive flagstaff, not very high. Nobody received the order to hoist our holy Merah-Poetih. Nothing was prepared. Nobody had thought in advance. Captain Latief, one of the few in uniform, stood near the flagstaff. Everybody waited tensed when he took the flag, fastened it to a thin frayed rope and let it fly... lonely... proud... for the first time in three and a half centuries.
There was no music, no band. After the flag was hoisted we just sung the 'Indonesia Raya'. (...)
It was ten o'clock [in the morning]. The Revolution had started."

From Sukarno by Cindy Adams, The Hague 1967.

Merah-Poetih simply means Red-White. The official name however is
Sang Saka, Lofty Bicolor. Red represents the human blood, standing
for the corporeal or concrete, white represents the spiritual. Together they
are a pair, like the life on earth: day and night; man and wife; creation and
induvidual.Mark Sensen, 21 May 1998

Traditionally almost all Indonesia since long ago use red & white as their sacred colours, resembling the colour of sugar (red in colour because the sugar comes from palm-sugar, "gula (sugar) aren (palm-
sugar)") and rice (white in colour). Both of these (rice & sugar) are the major components of daily Indonesian cuisine/cooking. When one of the tribes later became so powerful in the islands, that is the Javanese's Majapahit Empire, they did not forget this tradition. They used red-white colours as their National flag. Even today the Indonesians are still using red-white in their National Flag. So,
thousand years of unbroken history. Surprisingly, their distant cousins in Madagascar also use the "sacred colour of red & white" in their National Flag. Again, thousand years of unbroken
Ary Prihardhyanto Keim, 3 December 1999